September 29, 2022

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How do plants control the flow of water?  We learned poorly in school

How do plants control the flow of water? We learned poorly in school

All plants on Earth need water. But how many are there actually? Scientists have shown that up to 300 grams of water is needed to make each gram of dry plant matter. Australian scientists have discovered another important secret.

Scientists from the Australian National University and James Cook University have discovered the secret of plants that can help them grow with less water consumption. An article on this topic was published in Conversationand did a search nature plants.

water control

Plants are made up of 80% water. So you would expect them to need about 4 grams of water per gram of dry matter in order to maintain an optimal level of hydration. In order to produce 1 gram of new dry matter, the plant needs about 300 grams of water. Why is there such a difference between the amount of water needed to grow and stay hydrated? The reason is simple. Almost all water taken up from the soil by roots is released almost instantly into the atmosphere through the leaves (transpiration).

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Stomach transpiration occurs through stomata which consist of holes (the so-called stomata) surrounded by two stomata cells located in the leaf epidermis. The transpiration process itself begins with the evaporation of water from the surface of the cells of the assimilation crumbs – the water vapor formed in this way enters the air chamber and penetrates outside. Stomatal transpiration accounts for about 75-90% of the total transpiration.

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Scientists who study plants have long assumed that the opening and closing of the stomata almost completely controls the amount of water evaporated from the leaf. This is based on the assumption that the air in the small pockets inside the paper is completely saturated with water vapor (otherwise you can say that the “relative humidity” is 100% or close to this level). When the air inside the leaf is saturated and the air outside is drier, the stomata opening controls the amount of water that spreads out of the leaf. As a result, a large amount of water vapor is released from the leaf for each molecule of carbon dioxide that enters it.

Why did we assume that the air inside the leaves has a relative humidity close to 100%? Partly because the water moves from places that are more saturated to places that are less saturated, so we thought the cells inside the leaves couldn’t stay wet if they were directly exposed to air with a relative humidity well below 100%. But we also made this assumption because we didn’t have a way to directly measure the relative humidity of the air inside the leaves.We read in the conversation article

In the end the truth was revealed. A series of experiments over the past fifteen years have shown that the basic assumptions of botanists are incorrect. When the air outside the leaf was dry, the relative humidity in the air spaces inside the leaves routinely dropped below 100%, sometimes as high as 80%.

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What is striking, however, is that even under these conditions, photosynthesis did not stop or even slow down. The rate of water loss from the leaves remained constant. If leaves limit water loss by closing stomata, photosynthesis will slow down. However, plants have been shown to effectively control water loss from leaves, allowing proper diffusion of carbon dioxide into the interior of the plant.

Australian scientists believe that plants control the movement of water using proteins called aquaporins that are found in cell membranes within the leaf. Subsequent experiments will verify whether aquaporins are indeed responsible for this process.